The present invention relates to a method for treating biological waste, particularly household waste, by means of composting.
The invention also relates to an apparatus, i.e. a dry latrine, mainly for treating biological household waste by means of composting, which latrine comprises a bowl for the waste, the bottom part of the bowl being preferably formed as a trough, wherein is installed a spiral conveyor or other similar conveyor and at the end of which trough is located an opening through which the waste is discharged into a separate space where the composting takes place.
Several dry latrines are known which utilize a particular medium substance or covering substance such as peat, sawdust or bark waste. Generally these latrines are operated on the principle that each person using the latrine covers his leavings. This feature also causes the drawbacks of the prior art latrines based on the use of covering substances. The spreading of the covering substance is both inconvenient and unhygienic. Automatically operated covering devices have also been developed, but generally their operation has not succeeded in the desired fashion.
On the other hand, many latrines with covering substance do not function satisfactorily although the dosing problem of the covering substance is solved. The composting process is very slow. This is due to the fact that optimal conditions for composting are usually not achieved in these latrines.
For instance the Finnish Patent Publication No. 52846 introduces a biological latrine based on the use of medium substance, which latrine comprises a U-shaped collecting vessel provided with perforations at the bottom, which vessel is located in a closed space. Lengthwise in the middle of the collecting vessel there are installed mechanical mixer means for treating the mass. These mixer means are formed of an axis geared to rotate horizontally, and the axis is provided with radially protruding shafts of different lengths, which shafts are all bent in the rotating direction of the axis.
Below the collecting vessel there is arranged a pull-out container, whereto the compost soil processed in the collecting vessel can be dropped. In addition to this, the latrine is provided with a ventilation duct and a heating apparatus attached to the wall of the closed space.
The Finnish Patent Publication No. 54699 also introduces a biological latrine, where the composting chamber is realized as a U-shaped collecting bowl which is provided with similar mixer means as above. The chamber has a compact bottom and against the bottom there is installed an electric resistance foil which is protected by a heat insulator. The latrine can be provided with a thermostat placed within the chamber, and this thermostate regulates the heating resistor and prevents the temperature from rising too high with respect to the composting process. At the bottom of the chamber there is installed a moisture sensor which enables the regulation of the ventilation blower. In front of the composting chamber there is arranged a secondary chamber. Therebetween there is located a manually opened hatch through which the mass can be transferred from one chamber into the other.
In the medium substance latrines of the above patent publications, the purpose is to improve the composting conditions by means of the mixer means. However, these function ineffectively, and it seems probable that their use does not in practice lead to the desired result. For instance the discharge of the material from the composting chamber does not succeed by means of the described mixer means. The structure of the collecting vessel in these two examples does not ensure an effective aeration of the waste and the medium substance composition, even though the mixing should be improved. On the other hand it is pointed out that there is a trend to regulate the composting process by means of the thermostat and the moisture sensor.
The Finnish Patent Publication No. 63010 introduces a dry latrine where, at the bottom of the collecting vessel, there is arranged a trough whereinto a batch of the medium substance, for instance for two months, is charged all at the same time. The collecting vessel is provided with perforated end plates, and therebetween, at the bottom of the trough, there is placed the mixer spiral. The waste and the medium substance are mixed by means of the mixer spiral so that the mass is temporarily moved back and forth between the end plates, so that harmful process gases are exhausted and the mass is broken up into small lumps which are aerated effectively. Moreover, the process can be controlled by means of suitable sensors and a microprocessor, in which case the operation of the mixer, the ventilation, heat and moisture are accurately regulated. In addition to this there is located a discharge opening at the other end of the trough, through which opening the composted material can be discharged by means of the mixer spiral.
Irrespective of its several advantages, the above apparatus has two drawbacks. Firstly, the latrine must be regularly emptied and filled with the medium substance, although the operation periods are comparatively long. Secondly, the waste is treated and the waste is composted in the same space where it is put in the first place. In practice this is not a serious problem, but from the hygienic point of view it would be preferable if the composting proper should take place elsewhere. Generally speaking this applies for all the dry latrines described above.